This invention relates generally to systems for monitoring an EKG signal and estimating heartbeat rate, and, more particularly, to systems of this kind having means for reducing or eliminating the effects of heartbeat artifacts.
Heartbeat artifacts in an EKG signal can be caused by many factors, including poor continuity between electrodes attached to a patient and movement of the electrode leads. Systems having one electrode located in the patient's mouth are particularly susceptible to artifacts caused by movement of the mouth electrode. This is because use of mouth electrode creates a small battery potential between the electrodes, with any movement of the mouth electrode modulating this potential and thereby creating heartbeat artifacts.
Filtering the EKG signal to remove any heartbeat artifacts is not completely effective, because the artifacts and the actual heartbeart pulses have overlapping frequency spectra. Thus, filtering out the artifacts also filters out a substantial portion of the actual heartbeat pulses.
One technique for reducing the effects of heartbeat artifacts is described in a copending and commonly-assigned application for U.S. Pat. Ser. No. 410,043, filed in the name of Richard L. Foreman and entitled "Continuity Detector For Heartbeat Rate Measuring System." In the disclosed system, a pair of electrodes contact a patient to produce an EKG signal, and heartbeat detection means monitors the signal to detect the successive heartbeat pulses. A microprocessor measures the time intervals between the successive pulses, and estimates heartbeat rate based on those measurements. In addition, a special continuity circuit detects electrical continuity between the two electrodes and inhibits the microprocessor from measuring heartbeat intervals whenever poor continuity is detected. Although this system is generally effective in reducing the effects of heartbeat artifacts caused by poor electrical continuity, it is not believed effective in eliminating the effects of artifacts caused by factors other than poor continuity, such as by movement of the electrodes and electrode leads.
It should therefore be appreciated that there is a need for a heart rate monitoring system that further reduces the effects of heartbeat artifacts in an EKG signal. The present invention fulfills this need.